1. Field
The disclosure relates generally to a computer implemented method, a computer usable program code, and a data processing system. More specifically, the present disclosure relates to a computer implemented method, a computer usable program code, and a data processing system for controlling access to a contested resource.
2. Description of the Related Art
Increasingly large symmetric multi-processor data processing systems are not being used as single large data processing systems. Instead, these types of data processing systems are being partitioned and used as smaller systems. These systems are also referred to as logical partitioned (LPAR) data processing systems. A logical partitioned functionality within a data processing system allows multiple copies of a single operating system or multiple heterogeneous operating systems to be simultaneously run on a single data processing system platform. A partition, within which an operating system image runs, is assigned a non-overlapping subset of the platform's resources. These platform allocable resources include one or more architecturally distinct processors and their interrupt management area, regions of system memory, and input/output (I/O) adapter bus slots. The partition's resources are represented by the platform's firmware to the operating system image.
Each distinct operating system or image of an operating system running within a platform is protected from each other, such that software errors on one logical partition cannot affect the correct operation of any of the other partitions. This protection is provided by allocating a disjointed set of platform resources to be directly managed by each operating system image and by providing mechanisms for ensuring that the various images cannot control any resources that have not been allocated to that image. Furthermore, software errors in control of an operating system's allocated resources are prevented from affecting the resources of any other image. Thus, each image of the operating system, or each different operating system, directly controls a distinct set of allocable resources within the platform.
With respect to hardware resources in a logical partitioned data processing system, these resources are shared disjointly among various partitions. These resources may include, for example, input/output (I/O) adapters, memory DIMMs, non-volatile random access memory (NVRAM), and hard disk drives. Each partition within a logical partitioned data processing system may be booted and shut down over and over without having to power-cycle the entire data processing system.
Each distinct operating system or image of an operating system running within a platform is implemented using a partition management firmware, such as PowerVM, which is available from International Business Machines Corporation. In systems that contain a partition management firmware and many guest operating systems, performance is a major concern. Each guest operating system has at least one virtual central processing unit (VCPU). The partition management firmware controls access to a physical central processing unit (CPU) core by the guest operating systems and allocates time slices during which each VCPU gets to execute on the physical CPU core. It is often the case that the total number of VCPUs for all the guest operating systems is greater than the number of physical CPUs in the system.